Communication system for encrypted data and apparatus for selectively recording and reproducing received analog signal and received digital signal

ABSTRACT

A communication system has an analog signal broadcasting station for transmitting an analog signal, a digital signal broadcasting station for transmitting a digital signal and a receiving unit for receiving the analog signal from the analog signal broadcasting station and the digital signal from the digital signal broadcasting station. The receiving unit has a recording and reproducing unit for selectively recording one of received analog and digital signals. The recording and reproducing unit has heads for analog signal each having a predetermined azimuth angle and operative to record an analog signal and heads for digital signal each having an azimuth angle larger than that of the analog signal head and operative to record a digital signal, and performs selective recording and reproduction of the analog signal and the digital signal on and from a recording medium.

This application is a divisional of application Ser. No. 08/500,833,filed Jul. 11, 1995 now U.S. Pat. No. 5,903,104.

BACKGROUND OF THE INVENTION

The present invention relates to a communication system in whichcommunication is carried out through a communication medium such as acoaxial cable, an optical cable, a telephone circuit or satellitebroadcasting and an apparatus for recording and reproducing a signalcommunicated through the communication medium and more particularly, toa communication system for encrypted data and an apparatus forselectively recording and reproducing a received analog signal and areceived digital signal.

A technique concerning a system for encryption and decryption of a videosignal and an audio signal as well as fee charging is described in, forexample, “Transactions The Institute of Television Engineers of Japan”,Vol. 46, No. 1, January, 1992, pp. 31-39.

The above paper describes a technique concerning the system forencryption and decryption of a video signal and an audio signal as wellas fee charging in satellite communication service. However, that paperfails to disclose method and technique which can store a received signalwhile protecting a copyright of the signal and can charge fees ofdecryption and storage of the signal.

A technique of selecting a digital signal or an analog signal andrecording it on the same magnetic recording and reproducing apparatus isdescribed in, for example, JP-A-5-207507.

Available for a domestic magnetic recording and reproducing apparatus(hereinafter referred to as VTR) are, for example, VHS, β and 8millimeter-VTR standards. In any of these standards, an analogtelevision signal is FM modulated and then recorded. It is stipulatedthat an audio signal can also be FM modulated and recorded in accordancewith each standard. An apparatus for multiplexing, recording andreproducing analog video and audio signals in this manner is disclosedin U.S Pat. No. 4,591,924.

When a television signal is FM modulated for analog recording, therearises a problem that the S/N ratio is inevitably deteriorated owing torecording and reproduction. To cope with this problem, the televisionsignal is digitized and then recorded. For example, D-1, D-2 and D-3standards prescribed by SMPTE are available. These standards aredetermined by taking the use for broadcasting into account andtherefore, a tape cassette different from that used for theaforementioned domestic VTR is used under these standards.

The fact that quality of recording and reproduction is improved byrecording and reproducing a digital signal is desirable but when user'smerit is taken into consideration, it is preferable that theconventional analog signal be also recorded and reproduced. In otherwords, exchangeable reproduction of analog and digital signals must betaken into account.

This requires that at least the shape of a cassette to be used be thesame for analog and digital signals and the tape transport system bealso the same for analog and digital signals. Further, by making therecording and reproducing head or at least the azimuth angle of the headidentical for analog and digital signals, exchangeability can befacilitated and cost reduction can be ensured.

But it has been found that the above expedient faces a new problem. Forexample, when the digitally recorded cassette is inserted by mistakeinto the conventional analog VTR, the recorded digital signal ismistaken for an FM signal and is FM demodulated inadvertently.Especially when the FM demodulated signal is an audio signal, thedemodulated audio signal has a large amplitude and so large a sound thatpossibly surprises persons involved and damages the apparatus isgenerated from a loudspeaker.

The aforementioned conventional technique fails to show what problemarises when the digitally recorded cassette is loaded on theconventional analog VTR. Needless to say, the conventional techniquedoes not clarify how to solve the problem.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an apparatus forselectively recording and reproducing an analog signal and a digitalsignal.

Another object of the present invention is to provide a data receivingunit which can receive and decrypt or store an encrypted signal whileprotecting a copyright of the signal and which is suitable to chargefees of decryption and storage of the signal.

According to the present invention, in a recording and reproducingapparatus for selectively recording a digital signal and an analogsignal, there are provided a head for digital signal adapted to record adigital signal and a head for analog signal adapted to record an analogsignal, and the digital signal head has an azimuth angle which is largerthan that of the analog signal head.

Further, the digital signal head has a gap length which is smaller thanthat of the analog signal head.

Also, in a recording and reproducing apparatus for recording an analogtelevision signal of at least one of PAL, SECAM and NTSC schemes and adigital signal by using rotary heads carried on a cylinder, means forcontrolling the rotation of the cylinder is provided which controls therotation of the cylinder such that the rotation number of the cylinderduring recording the digital signal is substantially equal to thatduring recording the analog television signal of the NTSC type.

Further, in a recording and reproducing apparatus for azimuth recordingof a digital signal, an analog video signal and an analog audio signal,there are provided a head for digital signal, a head for analog videosignal and a head for analog audio signal, and the digital signal headhas an azimuth angle which is larger than that of the analog videosignal head but is smaller than that of the analog audio signal head.

By performing azimuth recording in which the azimuth angle is differentfor adjacent tracks, a reproduced signal from an adjacent track can besuppressed. In the reproduced analog signal processing in the VTR, thesignal processing is carried out in which a low frequency component of asignal from the adjacent track responsible for reduction of the azimutheffect is suppressed. Since the azimuth angle of the digital signal headis larger than that of the analog signal head, the azimuth effect can bepromoted and the low frequency component of the adjacent track signalcan be more suppressed during digital signal reproduction than duringanalog signal reproduction, thereby permitting recording andreproduction in which the error rate is reduced. In addition, by makingthe azimuth angle of the digital signal head smaller than that of theanalog audio signal head, the level of a reproduction signal from theanalog audio signal head can be decreased even when a digitally recordedtape is inserted into the analog VTR by mistake, thereby preventinggeneration of an abnormal sound.

Further, by making the gap length of the digital signal head smallerthan that of the analog signal head, high frequency recording andreproducing characteristics for a digital signal can be improved toensure recording at high density.

Further, by making the rotation number of the cylinder substantiallyidentical for digital signal recording and analog NTSC signal recording,control operation can be facilitated and the rotation number of thecylinder is larger for NTSC recording than for PAL or SECAM recording,thereby increasing the recording rate of a digital signal.

According to another specific form of the present invention, when in atransmitting apparatus a user requests transmission of desired data, akey signal is calculated from a predetermined initial value pursuant toan arithmetic formula corresponding to the user, the desired datarequested to be transmitted is encrypted on the basis of the key signalto form main data, and the main data is multiplexed with the initialvalue and a user identifying code so as to be transmitted.

In a receiving unit, on the other hand, the main data is demultiplexedfrom the initial value and the user identifying code, reception of therequired data requested to be transmitted by this receiving unit isconfirmed using the user identifying code, a key signal is generatedfrom the initial value pursuant to the arithmetic formula correspondingto the user, and the required data is decrypted from the main data onthe basis of the key signal.

Further, in the receiving unit, after reception of the required data isconfirmed, the main data can be multiplexed with the initial value so asto be recorded on a recording unit. Furthermore, when performingrecording on the recording unit, the initial value can be converted intoa key signal by using the arithmetic formula and thereafter the keysignal can be recorded.

In the receiving unit, permission of signal reception by a receptioncontractor is confirmed using a preset identifying code and thereafter,an initial value delivered out of input signal demultiplexing means issubjected to an arithmetic operation to generate a key signal. For aperson who is not the contractor, the correct key signal cannot beobtained from the initial value through the arithmetic operation. For auser who is not given permission of reception from a data distributor, acipher of main data cannot be decrypted because the main data isencrypted for only a user who is given permission of reception.

Here, the identifying code is a code which indicates that a distributorof a receiving signal allows a reception contractor to receive a signaland which is added to discriminate the present unit from another similardata receiving unit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram for explaining an overall communicationsystem according to the present invention of a multi-channel chargeabledigital broadcasting system utilizing a communication satellite and ananalog television broadcasting system.

FIG. 2 is a block diagram showing an embodiment of a transmitter in FIG.1.

FIG. 3 is a block diagram showing an embodiment of a receiver in FIG. 1.

FIG. 4 is a block diagram showing another embodiment of the receiver inFIG. 1.

FIG. 5 is a block diagram showing an embodiment of construction of acircuit for transmitting a transmission signal by multiplexing andencrypting the transmission signal in the transmitter of FIG. 1.

FIG. 6 is a block diagram showing an embodiment of a receiver forreceiving multiplexed encrypted data transmitted from the transmittershown in FIG. 5.

FIG. 7 is a block diagram showing another embodiment of the receiver forreceiving multiplexed encrypted data transmitted from the transmittershown in FIG. 5.

FIG. 8 is a block diagram showing an embodiment of a VTR arrangedattachably in the receiver of FIG. 1.

FIG. 9 is a block diagram showing an embodiment of a control circuit ofthe VTR shown in FIG. 8.

FIG. 10 is a diagram showing an embodiment of head arrangement in theVTR shown in FIG. 8.

FIG. 11 is a view showing, in developed strip form, the head arrangementof FIG. 10 realized on the periphery of a cylinder.

FIG. 12 is a diagram showing the relation between the track and theazimuth angle when data is recorded on a magnetic tape by using headsfor digital signal of FIG. 10.

FIG. 13 is a diagram showing another embodiment of head arrangement inthe VTR shown in FIG. 8.

FIG. 14 is a view showing, in developed strip form, the head arrangementof FIG. 13 realized on the periphery of a cylinder.

FIG. 15 is a diagram showing the relation between the track and theazimuth angle when data is recorded on a magnetic tape by using headsfor digital signal of FIG. 13.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A video distribution service using a satellite will be described as oneembodiment of the present invention with reference to FIG. 1.

The video distribution service is carried out by an operator who managesan operation center 20.The operator makes a contract with a softwaredistributor 10 to ask it to supply needful or required software to aprogram distribution center 30.In an embodiment shown in FIG. 1, onlyone software distributor 10 is depicted but typically, a plurality ofsoftware distributors can participate in supply of software.

The program distribution center 30 is provided with a transmitter 31which radiates an electric wave targeting on a satellite 40. Thesatellite 40 receives the electric wave and transmits it towards asubscriber 50. The transmitted electric wave is received by a receiver51.

The electric wave received by the receiver 51 is inputted to a receiverdecoder 52 which in turn selects software of a required channel. Theselected software is recorded on a VTR 53 as necessary. A signalcorresponding to the data recorded on the VTR 53 is reproduced whendesired and is returned to the receiver decoder 52 so as to be decodedthereby to the original video signal which in turn is delivered to atelevision 54.

By using a telephone set 55, the subscriber can also asks the operationcenter 20 to transmit software the subscriber wants to see. Theoperation center 20 can also research receiving and audience conditionsof the subscriber 50 from the receiver decoder 52 through a telephonecircuit and can charge a fee in compliance with audience conditions.

Further, an electric wave broadcasted from an existing broadcastingstation 35 by way of a transmitter 36 is received by a receiver 56 and areceived signal is inputted to the VTR 53 so as to be recorded thereon.A signal reproduced from the VTR 53 can be inputted to the television 54and can be watched. When recording on the VTR 53 is not needed, a signalfrom the receiver 56 can of course be inputted directly to thetelevision 54 so as to be watched.

Referring now to FIG. 2, details of the program distributor center 30are shown in block form. In FIG. 2, input means 100 receives softwaretransmitted from the software distributor 10 through a circuit and inputmeans 101 receives a signal for control of, for example, a transmissionprogram, the control signal being delivered out of the operation center20.

Programs can be supplied from the software distributor 10 to the programdistribution center 30 by using a circuit of, for example, opticalfiber, coaxial line or satellite. As the case may be, programs can bestored in a storage medium such as a VTR cassette or an optical diskwhich can be transported. With the circuit used to supply software, thesoftware is inputted to a receiving processing unit 110 through theinput means 100. In the receiving processing unit 110,the signalinputted through the circuit is processed for demodulation, errorcorrection or bit expansion as necessary. An output signal from thereceiving processing unit 110 is inputted to a switching unit 112 and astorage device 120. In the storage device 120, the inputted software isstored and conserved in a medium of the storage device 120. Whensoftware stored in a storage medium such as a VTR cassette or an opticaldisk is transported from the software distributor 10 to the programdistribution center 30, a storage device 111 complying with thetransported medium is used for reproduction. A program reproduced fromthe storage device 111 is inputted to the switching unit 112.

The switching unit 112 is switched in accordance with signal inputconditions to deliver an output signal which is inputted to a bitcompression unit 130. The bit compression unit 130 performs digitalcompression such as a so-called MPEG2 to decrease the amount of datanecessary for transmission. When data subject to digital compression issupplied from the software distributor 10, the bit compression unit 130can be omitted. An output signal of the bit compression unit 130 isinputted to a storage device 131. The storage device 131 can use amedium capable of performing recording and reproduction, for example, adigital VTR, an optical disk or a magnetic disk.

A signal for control of, for example, a predetermined broadcastingprogram or a transmission program complying with a request by asubscriber is inputted from the operation center 20 to a programcontroller 150 through the input means. Program transmission controlsignals from the program controller 150 are inputted to the storagedevices 120 and 131 and a transmitting processing unit 140. Softwaredelivered out of the storage device 120 is inputted to a bit compressionunit 121 so as to be subjected thereby to digital compression such as aso-called MPEG2, as in the case of the bit compression unit 130, todecrease the amount of data necessary for transmission. An output signalof the bit compression unit 121 is supplied to the transmittingprocessing unit 140. A signal delivered out of the storage device 131 isalso fed to the transmitting processing unit 140.

When it is desired that software be transmitted as soon as supplied fromthe software distributor 10, the software, which has once been recordedon the storage device 120, is not reproduced and delivered but an inputsignal to the storage device 120 may be delivered to the bit compressionunit 121 while being recorded on the storage device 120 as necessary.

When software supplied from the software distributor 10 isrepresentative of data which has already been subjected to bitcompression, there is no need of again passing the software through thebit compression unit 121.

The transmitting processing unit 140 performs encryption and addition ofan error correction code as necessary and responds to a control signalfrom the program controller 150 to modulate needed software with apredetermined carrier frequency, thereby delivering a modulated outputsignal. The output signal of the transmitting processing unit 140 isinputted to a transmitter 31. The transmitter 31 transmits a signaltargeting on the satellite 40 shown in FIG. 1.

The receiver coder 52 in the subscriber 50 is concretely constructed asshown in FIG. 3. There are provided in FIG. 3 an input terminal 200 forreceiving a signal from the receiver 51, an input/output terminal 201for transmitting and receiving a signal which is used to make a requestto the operation center for software and a signal which is necessary forknowing receiving conditions of chargeable broadcasting, an outputterminal 202 for delivery of a decompressed signal, an output terminal203 for delivery of a signal to the VTR, an input terminal 204 forreceiving a signal from VTR to receiver decoder 52, an input terminal205 for receiving a signal from the receiver 56 shown in FIG. 1, a tuner210, an error correction unit 220, a channel divider 230, a switchingcircuit 240, a decryption circuit 250, a decompression circuit 260 forbit expansion, an output processing circuit 270, and a control circuit280.

The receiver 51 receiving a signal from the satellite 40 delivers thereceiving signal to the tuner 210 through the terminal 200. Responsiveto a control signal from the control circuit 280, the tuner 210 selectsa signal of a channel for a program the operator wants to see anddemodulates the signal modulated by the transmitting processing unit 140to deliver a demodulated signal to the error correction circuit 220. Inaccordance with an error correction code added by the transmittingprocessing unit 140, the error correction circuit 220 corrects an errormainly caused in a circuit. An error-corrected signal is inputted to thechannel divider 230. When a plurality of programs are transmitted on asingle channel, the channel divider 230 responds to a control signalfrom the control circuit 280 as necessary to select and deliver adesired program.

The output signal of the channel divider 230 is inputted to theswitching circuit 240 and the VTR 53 through the output terminal 203. Inthe VTR 53, an input signal received in the form of a digital bit streamis recorded and when reproducing, a reproduced signal having the sameform as the input bit stream is inputted to the switching circuit 240through the input terminal 204. Responsive to a control signal from thecontrol circuit 280, the switching circuit 240 selects and delivers thesignal from the channel divider 230 when the received signal is to bereconstructed but selects and delivers the signal from the inputterminal 204 when the reproduced output signal from the VTR 53 is to beselected and delivered.

The output signal of the switching circuit 240 is supplied to thedecryption circuit 250. In the decryption circuit 250, the signalencrypted by the transmitting processing circuit 140 is decrypted. Asignal having its cipher decrypted and being delivered out of thedecryption circuit 250 is fed to the decompression circuit 260 in whichthe signal subjected to bit compression by the bit compression circuit121 or 130 shown in FIG. 2 or by the software distributor 10 shown inFIG. 1 is decompressed and expanded.

A signal subjected to bit expansion by the decompression circuit 260 isinputted, as a component signal consisting of a brightness signal andtwo color difference signals, to the output processing circuit 270. Inthe output processing circuit 270, the inputted two color differencesignals are subjected to quadratic two-phase modulation so as to beconverted into a carrier color signal, the resulting carrier colorsignal being delivered along with the brightness signal. The outputsignal is inputted to the television 54 through the output terminal 202.To meet the case where only a composite input terminal is provided forthe television 54, the output processing circuit 270 may add thebrightness signal to the carrier color signal to produce a compositesignal which is delivered. Further, both of a signal consisting of thebrightness signal and carrier color signal and a composite signal may bedelivered.

A signal delivered out of the receiver 56 and inputted through the inputterminal 205 is recorded on the VTR 53 as necessary and a reproducedsignal is delivered to the television 54. Alternatively, when recordingof the input signal is not effected, the input signal or a signalequivalent thereto is delivered to the television 54.

Referring now to FIG. 4, there is illustrated another specificembodiment of the receiver decoder shown in FIG. 1. In FIG. 4, part ofthe embodiment shown in FIG. 3 is improved. In the embodiment shown inFIG. 4, components identical to those of FIG. 3 are designated byidentical reference numerals.

The embodiment shown in FIG. 4 differs from the embodiment shown in FIG.3 in that a channel divider 230 is so moved as to follow a switchingcircuit 240. Namely, an output signal of an error correction circuit 220is inputted to a VTR 53 and the switching circuit 240 and an outputsignal of the VTR 53 is inputted to the switching circuit 240. Then, anoutput signal of the switching circuit 240 is sent to the channeldivider 230.

In the embodiment shown in FIG. 4, a plurality of (inclusive of one)programs transmitted on a single channel which is unaffected by channeldivision are recorded on the VTR 53. An output signal of the VTR 53 isinputted to the channel divider 230 through the switching circuit 240and one program is selected and delivered. In this case, a plurality ofprograms can be recorded on the single VTR at a time.

Next, a multiplexed communication system of encrypted data according tothe present invention will be described by way of a system utilizing acommunication satellite.

A user about to receive a multi-channel chargeable digital broadcastingservice first applies for admission to the program distribution center,i.e., a broadcasting station by mail or through the medium of acommunication circuit and at the same time, pays an entrance feethrough, for example, a banking organ cooperative with the broadcastingstation. After confirming the application for admission, thebroadcasting station assigns a user identifying number (hereinaftercalled a user ID) to the user and sends to the user, for example, anexclusive terminal registered with the user ID or an exclusive IC cardregistered with the user ID. The user opens a receiving terminal byusing the sent exclusive terminal or mounting the exclusive IC card to ageneral-purpose receiving terminal and is now ready to receive theservice.

For example, a multi-channel chargeable digital broadcasting systemutilizing an information compression technique can make use of a greatnumber of channels in the broadcasting system to offer a new servicesuch as time shift broadcasting in which identical programs are startedto be broadcast on a plurality of channels at different times which areat constant time intervals or video on demand. (hereinafter called aVOD) in which a program is broadcast at a request by a receivingterminal side. In addition, the broadcasting system utilizes a signal inthe form of a digital signal which is not deteriorated in the course oftransmission and reception and therefore, it can provide information ofhigh quality.

However, immunity from deterioration during transmission/receptionsuggests that a duplicate having the same quality as that of an originalcan be obtained with ease and there is a possibility that when manyduplicates are made without permission by a copyright holder, acopyright of the signal distributor may be infringed or the normalmanagement of chargeable broadcasting may be broken down. Accordingly,in order to protect a copyright of the signal distributor and ensure thenormal management of chargeable broadcasting, the broadcasting stationis required to scramble a program to be transmitted, that is, encrypt atransmitting signal.

Having the above in mind, the broadcasting station scrambles signals formovies, sports relay broadcast and the like and transmits the resultingsignals. When receiving a scrambled signal, a communication satelliteperforms the processing such as conversion of carrier frequencies ofreceiving and transmitting frequencies and transmits a signal to arequired service area including a receiving terminal. The receivingterminal being in receipt of an electric wave from the communicationsatellite (an exclusive terminal supplied from the broadcasting stationor an opened receiving terminal mounted with an exclusive IC card)releases the signal from scramble to permit a program to be viewed.

Then, the broadcasting station researches audience conditions of thechargeable program at the receiving terminal through, for example, acommunication circuit connecting the broadcasting station and thereceiving terminal, charges a fee, for example, monthly, every channelas contracted or for watched programs and collects an audience feethrough a banking organ.

Referring now to FIG. 5, an example of the construction of abroadcasting station comprised of the operation center 20 and programdistribution center 30 as shown in FIG. 1 will be described.

In FIG. 5, an input terminal 301 receives, through a bidirectionalcommunication circuit, an application for admission or a request forprogram by a receiving terminal, for example, the receiver decoder 52 ortelephone set 55 of FIG. 1, or information on audience conditionsnecessary for charging. Through an output terminal 302, a compressedmultiplexed program is transmitted to the communication satellite 40 ofFIG. 1.

In the multi-channel chargeable digital broadcasting system capable ofoffering a variety of new services by utilizing, for example, thecommunication satellite, the VCD is taken as an example of service andthe internal construction of the broadcasting station comprised of theoperation center 20 and program distribution center 30 of FIG. 1 will bedescribed herein with reference to FIG. 5.

When a request from the receiving terminal is received through the inputterminal 301, an information managing unit 314 first retrieves acustomer information data base 319 and checks whether a user who hastransmitted the request is a normal subscriber and checks payingconditions of audience fee. When a program is permissible for offeringto the user who has transmitted the request, the requested program isreproduced using a reproducing unit 311. The program reproduced by thereproducing unit 311 is compressed by a compression circuit 312 throughan optimum compression method meeting characteristics of theinformation, for example, an MPEG scheme if the program is of a video oraudio program, and is time-division multiplexed with a compressionsignal of a program requested by another user by means of atime-division multiplexing circuit 313.

The information managing unit 314 manages a predetermined initial valuefor generating a key signal necessary for encryption of a signal,delivers the initial value to a cipher generating circuit 315 and causesthe customer information data base 319 to deliver an arithmetic formulaand an identifying code to the cipher generating circuit 315. Typically,the same arithmetic formula may be used for individual subscribers butby changing the arithmetic formula every constant period or usingarithmetic formulas which are different for individual subscribers,safety of the system can be enhanced. The cipher generating circuit 315performs operation on the basis of the received initial value receivedfrom the information managing unit 314 pursuant to the arithmeticformula from the customer information data base 319 to calculate a keysignal and besides, generates data necessary for encryption of thesignal, for example, pseudo-random numbers.

On the basis of the above pseudo-random numbers, an encryption circuit316 encrypts the signal by performing, for example, exclusive ORing ofthe compressed multiplexed signal and the pseudo-random numbers orapplication of line rotation to the compressed multiplexed signal anddelivers the resulting signal as main data. Subsequently, a multiplexingcircuit 317 multiplexes the main data with the initial value of the keysignal, identifying code of the user and program information. Althoughnot described herein, encryption of the initial value of cipher, theidentifying code and the program information which are subjected tomultiplexing by the multiplexing circuit 317 can also be effected forthe sake of protecting privacy of the customer or preventing wrongdecryption of cipher, and hence safety of the system can be furtherimproved.

A transmitting circuit 318 carries out addition of an error correctioncode and packeting of data as well as the modulation processingnecessary for transmission of data to the communication satellite 40 andthen transmits the resulting data to the communication satellite 40through the output terminal 302.

Referring now to FIG. 6, an example of the internal construction of amulti-channel chargeable digital broadcasting receiving terminalutilizing the communication satellite will be described.

In FIG. 6, a receiving terminal corresponding to the receiver decoder 52of FIG. 1 receives a signal from the broadcasting station and performsthe signal processing. An input terminal 151 receives a signal from thecommunication satellite or the like. The signal is delivered to the VTR(data storage unit) 53 through an output terminal 152. An input terminal153 receives a signal delivered out of the VTR. An output terminal 154delivers the signal transmitted from the communication satellite or thelike or a signal in the form of a video or audio signal as a result ofdecryption of the signal delivered out of the VTR.

A signal responsive to a transmitted request is transmitted from thebroadcasting station through the communication satellite 40 and isinputted to the input terminal 151 of the receiving terminal 52 mountedwith an exclusive IC card 180. Although not illustrated in FIG. 6, anantenna installed, for example, in a room or outdoors is needed forreceiving an electric wave from the communication satellite 40 and thesignal received by the antenna is supplied to a receiving demultiplexingcircuit 161 through the input terminal 151. The receiving demultiplexingcircuit 161 first demodulates the receiving signal and corrects an errorof data or the like caused in a halfway communication circuit or thelike. Further, a user identifying code, an initial value of a key signalfor decryption of a cipher of main data, which are superimposed on thesignal, are demultiplexed and extracted from the encrypted main data.The initial value and the like are delivered to the exclusive IC card180 and the main data is delivered to a multiplexing circuit 166 and aselector 169.

The user identifying code inputted to the exclusive IC card 180 iscollated with a user ID stored in a memory 163 so that a managingcircuit 164 may confirm signal reception permission, confirm therequested program and extract the initial value of the key signal to theobjective program. Then, an arithmetic circuit 162 operates the initialvalue of the key signal to the objective program pursuant to specifiedalgorithm to calculate the key signal on the basis of the initial valueof the key signal. The arithmetic circuit 162 is precedently set withthe arithmetic algorithm which is identical to algorithm used in thecipher generating circuit 315 of FIG. 5 to calculate the key signal fromthe initial value thereof.

The key signal to the cipher is not transmitted from the broadcastingstation but only the initial value of the key signal, which is acompressed multiplexed signal, is transmitted and the key signal to thecipher is calculated through the arithmetic operation in the exclusiveIC card 180. This system permits a third person not having the exclusiveIC card 180 to receive the signal transmitted from the broadcastingstation but does not permit the third person to decrypt the cipher.Therefore, this system is effective to prevent wrong reception. Further,since the exclusive IC card 180 is detachably mounted to the receivingterminal 52 and is exchangeable, identical signals can be encrypted inaccordance with different kinds of algorithm. Moreover, since theexclusive IC card in the receiving terminal 52 has charge of allfunctions including management of the user ID, part of the receivingterminal excepting the exclusive IC card can be made in ageneral-purpose form and therefore, the use of the exclusive IC cardgives rise to advantages that the cost can be suppressed and thebroadcasting station need not manage the receiving terminal.

The key signal calculated by applying arithmetic operation to theinitial value in the arithmetic circuit 162 is delivered to anencryption circuit 165 and the selector 169. The encryption circuit 165encrypts the key signal by using the user ID delivered out of themanaging circuit 164 inside the exclusive IC card 180. Specifically, theuser ID is represented by, for example, a digital binary code andsubjected to the processing such as exclusive-ORing with the inputtedkey signal, and the resulting signal is delivered. It is to be notedthat the aforementioned user ID card is allotted to an individual whohas made a contract with the broadcasting station and remains unchangedeven when the exclusive IC card is exchanged.

The key signal encrypted by the encryption circuit 165 is multiplexedwith the main data delivered out of the receiving demultiplexing circuit161 by means of the multiplexing circuit 166 and the resulting signal isdelivered out of the output terminal 152. By recording the signaldelivered out of the output terminal 152 on the VTR 53, storage andconservation of the received signal can be ensured.

A signal delivered out of the VTR 53 is inputted to a demultiplexingcircuit 167 through the input terminal . 153. In the demultiplexingcircuit 167, the encrypted key signal and main data which have beenmultiplexed for recording on the VTR 53 are demultiplexed and the keysignal is delivered to a first decryption circuit 168 while the maindata being delivered to the selector 169.

In the first decryption circuit 168, the key signal encrypted by theencryption circuit 165 is decrypted. In the present embodiment, theencryption circuit 165 effects encryption by calculating exclusive-ORingof the key signal with the user ID stored in the memory 163.Accordingly, the first decryption circuit 168 decrypts the encrypted keysignal by also calculating exclusive-ORing of the user ID stored in thememory 163 with the inputted encrypted key signal.

Even when the exclusive IC card 180 is changed and arithmetic algorithmis changed during storage of data in the VTR 53, decryption of the maindata does not face any problem in the present system because the user IDremains unchanged and the signal encrypted by the encryption circuit 165is the key signal which does not require any arithmetic operation in thearithmetic circuit 162. Further, when it comes to preparing a duplicateof a receiving signal recorded tape by using a plurality of VTR's, thenormal user intending to prepare a duplicate for backup of a programreceived by himself or herself is allowed to perform correct decryptionif using the exclusive IC card supplied from the broadcasting station.But when a third person who is given a duplicate prepared for a wrongpurpose such as transfer uses an exclusive IC card different from theabove, a correct decryption result cannot be obtained. Accordingly, acopyright holder can be prevented from suffering damage by a wrongduplicate of a receiving signal.

The key signal decrypted by the first decryption circuit 168 is inputtedto the selector 169. Responsive to a command from a control circuit 172,the selector 169 selects one of the main data delivered out of thereceiving demultiplexing circuit 161 and main data delivered out of thedemultiplexing circuit 167 as well as one of the key signal deliveredout of the arithmetic circuit 162 and key signal delivered out of thefirst decryption circuit 168. More particularly, when the receivingdemultiplexing circuit 161 receives a signal requested by a user, theselector 169 responsive to the control circuit 172 selects and deliversthe main data delivered out of the receiving demultiplexing circuit 161and the key signal delivered out of the arithmetic circuit 162 but whenthe receiving demultiplexing circuit 161 does not receive any signal anda signal reproduced from the VTR 53 is inputted through the inputterminal 153, the selector 169 selects and delivers the main datadelivered out of the demultiplexing circuit 167 and the key signaldelivered out of the first decryption circuit 168.

On the basis of the key signal delivered out of the selector 169, arandom number generating circuit 170 generates pseudo-random numbers byusing the same procedure (or the same table) as that used by the ciphergenerating circuit 315 of FIG. 5 and delivers the resulting signal to asecond decryption circuit 171.

The second decryption circuit 171 decrypts the main data delivered outof the selector 169 by using the pseudo-random numbers delivered out ofthe random number generating circuit, that is, releases scramble appliedby the broadcasting station. Decryption of the main data is effected by,for example, calculating exclusive-ORing of the pseudo-random numbersgenerated from the random number generating circuit 170 with the maindata delivered out of the selector 169 or decrypting line rotation basedon the pseudo-random numbers.

A signal released from scrambling by means of the second decryptioncircuit 171 is subjected to the expansion processing inverse to thecompression processing applied by the compression circuit 312 of FIG. 5and the signal processing necessary for its delivery to the outside bymeans of an expansion circuit 173. More specifically, in the case of asignal compressed through MPEG scheme, the signal is expanded by an MPEGdecoder, subjected to the signal processing such as D/A conversion andscanning line conversion, delivered through the output terminal 154 anddisplayed on the monitor 54.

As described above, according to the aforementioned system of thepresent embodiment, by encrypting a key signal calculated from aninitial value of the key signal transmitted from the broadcastingstation by using a user ID, storage of a scrambled signal can be allowedonly when the user himself or herself intends to back up a signalreceived by himself or herself. Decryption of the signal can bepermitted unless a contract made with the broadcasting station iscanceled, that is, so long as the user ID is available. Further, sincethe stored signal cannot be subjected to decryption, expansion inverseto compression and display in the absence of an exclusive IC card storedwith a user ID, distribution of a duplicate to a third person can beprevented. In other words, while a copyright or the like of a signaldistributor is prevented from being infringed, decryption and storage ofsignals can be ensured.

When the number of signal receiving operations and hours thereof arestored by utilizing a memory provided in the receiving terminal 52 orthe memory 163 inside the exclusive IC card 180 and the broadcastingstation researches the communication circuit periodically or collectsand researches the exclusive IC card 180, a fee can be charged to thereceiving terminal 152 or the exclusive IC card 180 in accordance withutilization conditions. Further, signal receiving conditions such as,for example, audience conditions of program can be researched with ease.

Referring now to FIG. 7, another embodiment of the present inventionwill be described. In the Figure, components identical to those of FIG.6 are designated by identical reference numerals and will not bedescribed for avoiding prolixity of explanation.

In FIG. 7, a first selector 411 responds to a command from a controlcircuit 172 to select one of an initial value of a key signal deliveredout of a receiving signal demultiplexing circuit 161 and an initialvalue of a key signal delivered out of a demultiplexing circuit 167 anddelivers a selected initial value. A second selector 412 also respondsto a command from the control circuit 172 to select one of main datadelivered out of the receiving demultiplexing circuit 161 and main datadelivered out of the demultiplexing circuit 167 and delivers selectedmain data.

The receiving demultiplexing circuit 161 demodulates the receivedsignal, performs the signal processing such as correction of an error ofdata caused in a halfway communication circuit and thereafter,demultiplexes and extracts a user identifying code, the initial value ofthe key signal for decryption of a cipher of the main data from theencrypted main data. Then, in the present embodiment, the useridentifying code and initial value of the key signal are delivered to amultiplexing circuit 166 and the first selector 411 and the main data isdelivered to the multiplexing circuit 166 and the second selector 412.Further, the main data and the initial value of the key signal and thelike are multiplexed in the multiplexing circuit 166 and the resultingsignal is delivered through an output terminal 152 so as to be recordedon the VTR 53, thereby permitting storage of the signal.

A signal delivered out of the VTR 53 is inputted to the demultiplexingcircuit 167 in which individual signals multiplexed by the multiplexingcircuit 166 are demultiplexed, and the initial value of the key signaland the like are delivered to the first selector 411 and the main datais delivered to the second selector 412. The first and second selectors411 and 412 carries out an operation similar to that of the selector 169shown in FIG. 6. More particularly, responsive to a command from thecontrol circuit 172, the first and second selectors 411 and 412 selectand deliver the initial value of the key signal and the main datadelivered out of the receiving demultiplexing circuit 161, respectively,when the receiving demultiplexing circuit 161 receives a signalrequested by the user but select and deliver the initial value of thekey signal and the main data delivered out of the demultiplexing circuit167, respectively, when the receiving demultiplexing circuit 161 doesnot receive any signal and a signal reproduced from the VTR 52 isinputted through an input terminal 153.

Like the embodiment of FIG. 1, in the exclusive IC card 180, a signaldelivered out of the first selector 411 and representative of theinitial value of the key signal and the like is collated with a user IDhaving individual information stored in a memory 163 so that a managingunit 164 may confirm signal reception permission, confirm the requestedprogram and extract the initial value of the key signal to the objectiveprogram. An arithmetic circuit 162 operates the initial value of the keysignal to the objective program pursuant to specified algorithm tocalculate the key signal on the basis of the initial value of the keysignal. Like the foregoing embodiment, the arithmetic circuit 162 isprecedently set with the arithmetic algorithm which is identical to thatused in the cipher generating circuit 315 of FIG. 5 to calculate the keysignal from the initial value thereof.

Since the user ID is confirmed by being collated with the individualinformation transmitted from the broadcasting station and the key signalis then calculated in the exclusive IC card, calculation of the keysignal is allowed only for a signal received by the user himself orherself and a signal received, recorded and stored by himself or herselfand hence the copyright holder can be prevented from sufferingdisadvantage caused by a wrong duplicate.

Thereafter, as in the foregoing embodiment, the main data and the keysignal calculated in the exclusive IC card are subjected to the signalprocessing such as generation of pseudo-random numbers, decryption ofthe cipher of the main data and expansion of the compressed signal in apseudo-random number generating circuit 170, a decryption circuit 171and an expansion circuit 173 and are then displayed on the monitor 54.

As described above, according to the system of the present embodiment,by recording the initial value of the key signal transmitted from thebroadcasting station on the VTR along with the main data, decryption ofthe scrambled storage signal can be allowed only when the user views thesignal received by himself or herself. But, in the system of the presentembodiment, when the exclusive IC card is changed by changing thearithmetic formula delivered out of the customer data base 319, theinitial value of the key signal recorded on the VTR remains unchangedand only the arithmetic algorithm in the arithmetic circuit 162 ischanged, thus making it impossible to decrypt the main data. Therefore,in the system of the present embodiment, the period allowed for storageof signal is limited but similar effects to those by the foregoingembodiment can be obtained in connection with, for example, research ofaudience conditions and fee charge. Also, in the present embodiment, thereceiving terminal can dispense with the encryption and decryptioncircuits for key signal and extraction of the user ID from the exclusiveIC card, thereby attaining an advantage that the signal processingcircuit can be reduced greatly in scale.

In the foregoing embodiments, the communication circuit on which aprogram is transmitted is described by way of the communicationsatellite but it may be practiced with other communication circuits, forexample, a wire communication circuit using an optical fiber or acoaxial cable and a telephone circuit such as ISDN (integrated servicedigital network). Further, the data storage unit is not limited to theVTR but it may be realized with an optomagnetic disk unit, an opticaldisk unit, a hard disk unit or a large-capacity memory array. Inaddition, the signal to be transmitted is not limited to the videosignal and it may be audio information, character information or gamesoftware provided that it is of a binary code signal, i.e., a digitalsignal, and the compression system in the broadcasting station (signaldistributor) and the expansion system in the receiving terminal are notlimited to the MPEG but compression algorithm most suited to a signal tobe transmitted may be employed.

In the embodiments of FIGS. 6 and 7, the exclusive IC card is detachablymounted but a system is conceivable in which an exclusive IC card ismade to be integral with the receiving terminal, that is, the receivingterminal is made to be an exclusive receiving terminal which has anidentifying code and which has the function of managing the useridentifying code and arithmetic operation of the key signal. In thiscase, allotment of a user ID to each receiving terminal and managementof the receiving terminal by the broadcasting station are needed but onthe other hand, the control circuits carried on both the exclusive ICcard and the receiving terminal can advantageously be unified to asingle control circuit. Conceivably, the receiving terminal and the datastorage unit can be unified, that is, the VTR can be given the functionof the receiving terminal and in this case, effects similar to those bythe foregoing embodiments can be attained and besides, space reductionand wiring simplification can be ensured.

Referring now to FIG. 8, there is illustrated in block form anembodiment of the VTR 53. In FIG. 8, there are provided an inputterminal 350 for receiving a signal from the receiver decoder 52 shownin FIG. 1, an output terminal 351, an input terminal 352 for receiving asignal from the receiver 56 shown in FIG. 1 and an output terminal 353.

A signal received through the input terminal 350 is inputted to apre-processing circuit 360. In the pre-processing circuit 360, the inputdigital signal is processed to undergo rearrangement for word unitprocessing as necessary so as to facilitate the succeeding signalprocessing. An output signal of the pre-processing circuit 360 isinputted to a parity adding circuit 361. In the parity adding circuit361, a parity code for correcting an error caused in a tape transportsystem 320 is added. An output signal of the parity adding circuit 361is inputted to a modulation circuit 362. In the modulation circuit 362,the digital signal is modulated into a form suitable for the tapetransport system 320. Reported as examples of modulation systems areNRZ, NRZI, 8-10 conversion, MFM and M2. A modulated signal is inputtedto the tape transport system 320 so as to be recorded on a magnetictape.

During reproduction, a reproduced signal is inputted to a demodulationcircuit 330 and is demodulated correspondingly to the modulation circuit362. An output signal of the demodulation circuit 330 is inputted to anerror correction circuit 331 so as to be corrected for an error causedin the tape transport system 320 on the basis of the parity code addedby the parity adding circuit 361. An output signal of the errorcorrection circuit 331 is inputted to a post-processing circuit 332 soas to be subjected to the processing inverse to that applied by thepre-processing circuit 360 and a signal having the same form as that ofthe signal inputted through the input terminal 350 is delivered throughthe output terminal 351. The signal delivered out of the output terminal351 is inputted to the receiver decoder 52 shown in FIG. 1.

As shown in the embodiment of FIG. 8, there is no need of providing thebit compression circuits 121 and 130 as shown in FIG. 2 inside the VTR53 and therefore a digital signal recording VTR of small circuit scalecan be realized. In addition, the VTR need not have the internal bitcompression circuits but the software distributor 10 or the programdistribution center 30 may have the bit compression circuit andtherefore, a bit compression circuit of high performance can be used,though the circuit scale becomes large and the cost rises, with theresult that a relatively large bit compression ratio can be obtained todecrease the data rate of a digital signal to be transmitted.Accordingly, the VTR 53 used by the subscriber can ensure high quality,low cost and long-term recording.

An analog signal from the receiver unit 56 is inputted through theterminal 352 and supplied to an analog video signal recording processingcircuit 340 and an analog audio signal recording processing circuit 346.Here, the signal processing pursuant to, for example, VHS standard, βstandard or 8-millimeter VTR standard is carried out. A processed signalis inputted to the tape transport system 320. In the tape transportsystem 320, the signal is recorded in accordance with a correspondingformat as in the case of the conventional VTR.

During reproduction, a signal reproduced from the tape transport system320 is inputted to an analog video signal reproduction processingcircuit 345 and an analog audio signal reproduction processing circuit347 which apply to the signal the reproduction signal processingcorresponding to the analog video signal recording processing circuit340 and the reproduction signal processing corresponding to the analogaudio signal recording processing circuit 346, respectively. A needfulreproduced signal is inputted to the television 54 shown in FIG. 1through the output terminal 353. Through this, the digital broadcastingand the conventional analog broadcasting can be recorded using the sametape transport system.

Referring now to FIG. 9, there is illustrated in block form an exampleof a servo circuit for controlling a cylinder (included in the tapetransport system 320 in FIG. 8) and a capstan (also included in the tapetransport system 320 in FIG. 8) which constitute the tape transportsystem.

In FIG. 9, the mode of recording an analog signal will first bedescribed. In the case of recording an analog signal, a verticalsynchronizing signal is inputted through a terminal 400. The verticalsynchronizing signal is separated in the analog video signal recordingprocessing circuit 340 shown in FIG. 8. The vertical synchronizingsignal inputted through the terminal 400 is supplied to a switchingcircuit 411. In this mode, the switching circuit 11 delivers thevertical synchronizing signal inputted through the terminal 400. Thesignal delivered out of the switching circuit 411 is supplied to a ½frequency divider circuit 412 so as to be subjected to ½ frequencydivision. A ½ frequency divided signal is sent to a phase servo circuit421 of the cylinder system and phase servo circuit 431 and switchingcircuit 453 of the capstan system.

A cylinder motor 424 is rotated by a motor driver 423. The cylindermotor 424 is provided with a sensor for detecting rotation frequency androtation phase. A rotation frequency detected by the cylinder motor 424is supplied to a velocity servo circuit 420. Responsive to the rotationfrequency supplied from the cylinder motor 424, the velocity servocircuit 420 delivers a signal representative of a difference between thedetected rotation frequency and a predetermined frequency. Thedifference signal is supplied to an adder circuit 422.

A rotation phase detected by the cylinder motor 424 is supplied to thephase servo 421. The phase servo 421 compares a signal supplied from the½ frequency divider circuit 412 with the phase of the cylinder motor anddelivers a signal representative of a difference therebetween. Theoutput signal is supplied to the adder circuit 422 and added with thedifference signal delivered out of the velocity servo. An output signalof the adder circuit 422 is supplied to the motor driver 423 to controlthe cylinder motor 422 such that the cylinder motor 422 is phase-lockedwith the signal supplied from the ½ frequency divider circuit 412. Thevelocity servo 420 controls the rotation frequency of the cylinder motor424 to a constant value and the phase servo 421 performs fine control ofeven the phase of the cylinder motor 424.

The capstan system operates in substantially the same manner. A capstanmotor 434 is rotated by a motor driver 433. The capstan motor 434detects its rotation frequency which is supplied to a velocity servocircuit 430. The velocity servo circuit 430 compares the rotationfrequency of the capstan motor 434 with a predetermined frequency anddelivers a difference signal which is supplied to an adder circuit 432.

The rotation frequency of the capstan motor 434 is supplied to a 1/Nfrequency divider circuit 451. A frequency divided signal is fed to aswitching circuit 450. In this mode, the switching circuit 450 is sotransferred as to deliver the signal from the 1/N frequency dividercircuit 451. The output signal of the switching circuit 450 is suppliedto the phase servo circuit 431. The phase servo circuit 431 compares aphase of the signal from the ½ frequency divider circuit 412 with thatof the input signal from the switching circuit 450 and delivers adifference signal to the adder circuit 432.

The adder circuit 432 adds the difference signal from the velocity servocircuit 430 and the difference signal from the phase servo circuit 431to generate a sum signal which is delivered to the motor driver. Themotor driver controls the capstan motor 434 such that the capstan motor434 is phase locked with the signal from the ½ frequency divider circuit412.

Further, the signal of ½ frequency divider circuit 412 fed to theswitching circuit 453 is so selected thereby as to be supplied to acontrol head 454, with the result that a control signal is written ontoa magnetic tape.

During reproduction, a reference signal is inputted through a terminal401 and supplied to a frequency divider circuit 410. The frequencydivider circuit 410 divides the frequency of the input reference signalto deliver a signal of the same frequency as that of the verticalsynchronizing signal during recording. The output signal of thefrequency divider circuit 410 is supplied to the switching circuit 411.In this mode, the switching circuit 411 selects and delivers the outputsignal of the frequency divider circuit 410. The output signal of theswitching circuit 411 is supplied to the ½ frequency divider circuit 412and a resulting ½ frequency-divided signal is supplied to the phaseservo circuits 421 and 431.

The cylinder system operates in the same way as that for recording andthe cylinder is phase locked with the input signal from the ½ frequencydivider circuit 412.

The capstan system will now be described. During reproduction, thecontrol signal written during recording is reproduced from the magnetictape by way of the control head 454 and supplied to the switchingcircuit 453. During reproduction, the switching circuit 453 delivers thereproduction signal from the control head 454 to a waveform shapingcircuit 452. In the waveform shaping circuit 452, the waveform of theinput signal is shaped by, for example, being passed through acomparator. A shaped signal is fed to the switching circuit 450 and inthe reproduction mode, the switching circuit connects the signal fromthe waveform shaping circuit 452 to the phase servo circuit 431. Thephase servo circuit 431 carries out control operation such that thecontrol signal on the magnetic tape is phase locked with the signal fromthe ½ frequency divider circuit 412. Through this, the magnetic headhaving the magnetic tape carried on a cylinder can be scanned at thesame phase for both recording and reproduction operations and the signalon the magnetic tape can be reproduced.

Operation for controlling the cylinder and capstan carried out when ananalog signal is inputted has been described. Operation of the servocircuit shown in FIG. 9 carried out when a digital signal is inputtedthrough the terminal 350 in the embodiment of FIG. 8 will now bedescribed.

During recording, a reference signal is inputted through the terminal401 and supplied to the frequency divider circuit 410. The frequencydivider circuit divides the frequency of the input signal to a suitablevalue and a frequency divided output signal is fed to the switchingcircuit 411. When the VTR 53 is used for recording/reproducing thedigital signal, the switching circuit 411 selects and delivers thesignal of the frequency divider circuit 410. The output signal of theswitching circuit 411 is fed to the ½ frequency divider circuit 412.During recording, as in the case of recording of an analog signal, thecylinder and capstan are locked with the output signal of the ½frequency divider circuit 412.

By selecting the frequency of the reference signal supplied from theterminal 401 and the frequency division ratio of the frequency dividercircuit 410 to suitable values, the frequency of output signal of the ½frequency divider circuit 412 can be set to a desired cylinder rotationfrequency. By setting the tape running velocity to a desired value bymeans of the velocity servo circuit 430 and setting the frequencydivision ratio of the 1/N frequency divider circuit 451 in compliancewith the frequency of output signal of the 112 frequency divider circuit412, the tape can be run at a required velocity. Further, by making thefrequency of output signal of the frequency divider circuit 410substantially equal to the vertical synchronizing frequency of the videosignal, the rotation number of the cylinder carrying the magnetic tapecan be made to be equal to that for recording an analog signal. Sincethe cylinder is so designed that at the rotation number for recording ofan analog signal, physical conditions between the cylinder and themagnetic tape are optimized, good contact can be obtained between themagnetic head and the magnetic tape and excellent recordingcharacteristics can be ensured. By making the frequency division ratiosmaller and making the output signal frequency of the frequency divisioncircuit 410 higher, the rotation frequency of the cylinder can beincreased easily to increase the relative velocity between the magnetichead and the magnetic tape and accordingly, even a signal at a highrecording rate can be recorded.

During reproduction, by selecting the frequency of the reference signalinputted through the terminal 401 and the frequency division ratio ofthe frequency divider circuit 410 to suitable values, the signalfrequency of the frequency divider circuit 410 can be made to be equalto that for recording. Through this, both of the cylinder system and thecapstan system can be operated in the same way as that for reproducingan analog signal and the cylinder can be phase locked with the outputsignal of the ½ frequency divider circuit 412. Further, by switching theswitching circuits 450 and 453, the control signal reproduced from themagnetic tape can be phase locked with the output signal of the ½frequency divider circuit 412. In this manner, the same signal as thatfor recording can be reproduced from the VTR 53.

Table 1 shows examples of the rotation number of the cylinder. Whenrecording an analog signal, the rotation number of the cylinder is about1800 r.p.m. in the case of the input signal being an NTSC signal. Whenthe input signal is of a PAL or SECAM, the field frequency of the signalis 50 Hz and therefore, the rotation number is about 1500 r.p.m.Obviously, the same values of the rotation number are available duringreproduction. When recording a digital signal, the rotation number ofthe cylinder is about 1800 r.p.m. in the case where the number ofscanning lines is 525 per frame and the field frequency is 59.94 Hz(indicated at column of NTSC in Table 1) and also in the case where thenumber of scanning lines is 625 per frame and the field frequency is 50Hz (indicated at column of PAL/SECAM in Table 1).

TABLE 1 Rotation Number of Cylinder NTSC PAL/SECAM Analog recording 1800rpm 1500 rpm Digital recording 1800 rpm 1800 rpm

For both the system having the scanning line number being 525 and thesystem having the scanning line number being 625, the sampling frequencyis usually selected to 13.5 MHz. Accordingly, on the assumption that thecompression ratio is the same for both the systems, the transmissionrate of data is the same for both the systems. Therefore, the rotationnumber is not required to be changed in accordance with the fieldfrequency and when equality of the rotation number is desired to bemaintained, the rotation number is set to around 1800 r.p.m. as shown inTable 1 corresponding to a higher field frequency which can permitrecording of signals of higher rate. As has already been described, therotation number of the cylinder can be determined by the frequency ofthe reference signal inputted through the terminal 401 and the frequencydivision ratio of the frequency divider circuit 410 in the embodimentshown in FIG. 6.

When the rate of a digital signal to be recorded is low, the rotationnumber of the cylinder can otherwise be selected to about 1500 r.p.m. Inthis case, the recording time can be prolonged.

As described above, recording and reproduction of an analog signal canbe controlled in a similar manner to that for controlling in theconventional VTR. Further, it has been demonstrated that recording andreproduction of a digital signal can be effected in a similar manner tothat for analog signal VTR by using the same tape transport system.

In the case of recording a digital signal, it has been found that whenthe same head as that for recording an analog signal is used andsubstantially the same cylinder rotation number and tape velocity asthose for recording an analog signal are employed in order to suppressaddition of head and changes in circuit, the following problem arises.

More particularly, when a digitally recorded tape is reproduced with theconventional analog VTR, a digital signal is FM demodulated anddelivered in the form of a noise. Especially, when the output noisetakes the form of an audio signal, this signal is delivered at a signallevel up to the limit of a dynamic range, causing a loudspeaker togenerate a large sound which surprises persons involved and possiblydamages the apparatus.

A solution to this problem is to prevent a digital signal in excess of apredetermined level from being supplied continuously to an FMdemodulator. This expedient is realized with the present invention asfollows.

The azimuth angle of a head for recording a digital signal is made to bedifferent from that of a head for recording an analog audio signal.Through this, when a tape recorded with a digital signal is reproducedwith an analog VTR, a reproduced signal decreases in level and theanalog head can act as a mute circuit for audio signal. To ensure asteady audio mute function, it is necessary that the azimuth angle ofthe head for digital signal differ from that of the analog head forrecording audio signal by at least ±5°, preferably, ±10° or more. Aformula for calculating the attenuation degree of reproduced signal dueto the azimuth effect has been determined theoretically.

Referring now to FIG. 10, an example of arrangement of heads on acylinder when the VHS standard is presupposed. In FIG. 10, heads SP1 andSP2 are used for a so-called standard play mode during recording andreproduction of an analog video signal, heads EP1 and EP2 are used for aso-called super long play mode during recording and reproduction of ananalog video signal, heads HF1 and HF2 are used for recording andreproduction of an FM audio signal, and heads DP1 and DP2 are used forrecording and reproduction of a digital signal. In the Figure, a plus orminus sign indicates the direction of inclination of an azimuth angle ofeach head.

With the head arrangement shown in FIG. 10, when an analog signal isinputted, a video signal and an audio signal can be FM modulated andrecorded in the standard play mode or super long play mode. Even when adigital signal is inputted, it can be recorded using the exclusive headsDP1 and DP2 each having an azimuth angle different from that of the headfor analog signal recording. Thus, thanks to the fact that the azimuthangle differs for recording and reproduction even when a digitallyrecorded tape is reproduced by the analog VTR, a large reproductionlevel is not generated and the audio signal is muted to prevent anabnormal sound from being delivered and the apparatus from beingdamaged.

When the same magnetic tape is desired to be used for analog signalrecording and digital signal recording, recording efficiency can bepromoted by making the maximum frequency equal for the two kinds ofsignal recording.

In the case of a VTR of the VHS scheme, the FM carrier frequency of abrightness signal is 3.4 MHz for the synchronizing signal portion and4.4 MHz for a 100% white signal. Practically, however, emphasis isapplied to emphasize higher frequencies with a view of improving the S/Nratio, with the result that a signal in excess of 100% white signallevel is inputted at an edge of a rectangular wave and a side-band waveof the higher frequency component is also transmitted to a certainextent. Therefore, a signal at 6 MHz can be considered to be transmittedsteadily and when recording and reproducing a digital signal, recordingand reproduction at a maximum of about 12 Mbps can be permitted.

Further, by using the exclusive heads for digital recording as in thecase of the embodiment shown in FIG. 10 and designing the head gap forsuitability to digital signal recording, recording efficiency canfurther be promoted. For example, by using a tape for high picturequality prescribed by the S-VHS format for digital signal recording,recording at higher density can be ensured. In the case of a VTR of theS-VHS scheme, the FM carrier frequency of the brightness signal is 5.4MHz for the synchronizing signal portion and 7.0 MHz for a 100% whitesignal. Furthermore, since in the S-VHS the clip level of a signal isset to a high value, the maximum frequency allowed for practicalrecording and reproduction is 9 to 10 MHz. Accordingly, the maximumtransmission rate allowed for recording and reproduction of a digitalsignal is about 18 to 20 Mbps. The tape used in the S-VHS scheme is madeof a magnetic material having a larger coercive force than that of thetape used in the VHS scheme and hence recording at high density can berealized.

Table 2 shows examples of the azimuth angle, head width, gap length andtrack pitch of each head in that case. A head for digital signalrecording has a larger azimuth angle than a head for analog, videosignal recording. In the analog video signal reproducing processing, across talk component affected by an adjacent track is suppressed bymeans of an interdigital filter at a color signal portion at which theazimuth effect is decreased. But for the digital signal which is notallowed to undergo the processing as above, an exclusive head isprovided having a large azimuth angle, thereby ensuring that alow-frequency cross talk component from an adjacent track can besuppressed to decrease an interfering signal component from the adjacenttrack and the error rate can be decreased. By making the gap length ofthe head for digital signal recording smaller than that of other heads,recording efficiency of high frequency signal can further be promotedand recording at high density can be ensured. In addition, in theembodiment shown in Table 2, the track pitch for digital signalrecording is made to be about half the track pitch for standardrecording of analog signal. Through this, the S/N ratio well balanceswith the recording time, thus improving the recording density andprolonging the recording time.

TABLE 2 Azimuth Head angle Head width Gap length Track pitch HF1,HF2±30° 28 μm  1.1 μm 19/58 μm   SP1,SP2  ±6° 48 μm 0.35 μm 58 μm EP1,EP2 ±6° 26 μm 0.35 μm 19 μm DP1,DP2 ±15° 40 μm 0.23 μm 29 μm

Determination of the track pitch during digital signal recording hasrelation to the recording rate of a digital signal (namely, the maximumfrequency to be recorded) and the track pitch is so determined that arequired S/N ratio can be obtained at the maximum frequency. When amagnetic tape comparable to a tape pursuant to the S-VHS is used and therecording rate is set to about 18 to 20 Mbps, a practically acceptableerror rate can be obtained by setting the track pitch to about 29microns.

In Table 2, the track pitch of the heads HF1 and HF2 for recording an FMaudio signal is described as 19/58 microns, indicating that the trackpitch is 58 microns in the standard play mode and is 19 microns in thesuper long play mode.

Referring to FIG. 11, the periphery of the cylinder is developed instrip form to schematically show the positional relation between theindividual heads arranged on the cylinder as shown in FIG. 10 and eachhaving geometrical dimensions as described in Table 2. Shown in FIG. 12is the relation between the track and the azimuth angle when a digitalsignal is recorded on the magnetic tape. In FIG. 11, the heads foranalog recording EP, SP and HF are dimensioned and arranged as shown butthe heads for digital recording DP are illustrated as being displaced toan upper portion. Practically, however, the heads for digital recordingDP are arranged with their lower ends displaced from the lower ends ofthe heads for analog recording SP by, for example, 17 microns.

The azimuth angle of the heads, for digital recording is set to ±15°.According to the VHS standard, the exclusive head is used for FM audiosignal recording and its azimuth angle is ±30°. Since the head fordigital recording must have an azimuth angle which differs from that ofthe exclusive head for FM audio signal recording by at least ±5°, theazimuth angle of the head for digital recording must be more than 35° orless than 25°. With the azimuth angle increased, the effective relativevelocity between the tape heads can be decreased to advantage.Contrarily, with the azimuth angle deceased, when reproducing a digitalsignal, a low frequency signal from an adjacent track is reproduced todecrease the S/N ratio of a reproduced signal and recording at highdensity is difficult to achieve. Here, the azimuth angle of the head fordigital signal recording is selected to ±15° which is less than 25° andis expectant of the azimuth effect. Preferably, absolute value of theazimuth angle of the head for digital signal may be set to lie betweenabout 10° and about 20°.

Referring to FIG. 13, there is illustrated another embodiment of thehead arrangement. In the embodiment shown in FIG. 13, two sets of headsfor recording and reproducing a digital signal are provided for thepurpose of increasing the amount of data, representative of a digitalsignal, which can be recorded per unit time. In FIG. 13, heads DQ1 andDQ2 are for recording and reproduction of a digital signal. In theembodiment constructed as shown in FIG. 13, signals are recordedsimultaneously by means of a set of two heads DP1 and DP2 or the set oftwo heads DQ1 and DQ2. Therefore, as compared to the embodiment shown inFIG. 10, the amount of data which can be recorded per unit time can bedoubled. Table 3 shows the azimuth angle, head width, gap length andtrack pitch of each head used in this embodiment.

TABLE 3 Azimuth Head angle Head width Gap length Track pitch HF1,HF2±30° 28 μm  1.1 μm 19/58 μm   SP1,SP2  ±6° 48 μm 0.35 μm 58 μm EP1,EP2 ±6° 26 μm 0.35 μm 19 μm DP1,DP2 ±15° 40 μm 0.23 μm 29 μm DQ1,DQ2 ±15°40 μm 0.23 μm 29 μm

The periphery of the cylinder carrying the heads arranged as shown inFIG. 13 and each having geometrical dimensions as shown in Table 3 isdeveloped in strip form as shown in FIG. 14. When a digital signal isrecorded on a magnetic tape with the heads arranged as above, a trackpattern as shown in FIG. 15 can be obtained.

In this case, too, the azimuth angle of each head for digital signalrecording is selected to ±15° for the same reasons as above. Throughthis, effects similar to those of the examples shown in Table 2 can beattained.

Further, when tracking control is carried out in common to the case ofanalog recording and the case of digital recording by using a controlsignal as described in connection with the embodiment shown in FIG. 6,the control circuit can be used in common to thereby reduce the cost.

By making the azimuth angle of the head for digital signal larger thanthat of the head for analog video signal recording, the error rate of adigital signal can be decreased.

In addition, by making the gap length of the head for digital signalsmaller than that of the head for analog signal, high frequencycharacteristics of digital signal recording and reproduction can beimproved to thereby reduce the error rate of a digital signal.

By making the rotation number of the cylinder during digital signalrecording substantially equal to that of the cylinder during analog NTSCrecording, control operation can be simplified and the recording ratecan be increased.

By making coercive force-of the magnetic recording medium for digitalsignal recording larger than that of the magnetic recording medium foranalog signal recording, the recording rate of a digital signal can beincreased.

By making the azimuth angle of the head for digital signal differentfrom that of the head for analog audio signal recording by at least ±5°,generation of abnormal sounds can be prevented even when a digitallyrecorded tape is inserted into the conventional analog VTR.

What is claimed is:
 1. An apparatus for transmission of encrypted datacomprising: a memory for storing a plurality of customer identifyingcodes and arithmetic formulas set for individual customers; means forreproducing data requested for transmission by a customer; means forreading a customer identifying code and an arithmetic formula of thecustomer requesting transmission and generating an initial value; meansfor operating the initial value pursuant to said read-out arithmeticformula to calculate a key signal; encrypting means for encrypting datafrom said reproducing means on the basis of the key signal from saidcalculating means to generate main data to be transmitted; and means formultiplying said main data with said initial value and said customeridentifying code and transmitting a resulting signal.
 2. Thetransmitting apparatus according to claim 1, wherein said reproducingmeans is means for reproducing a plurality of pieces of data requestedfor transmission by a plurality of customers, said apparatus furthercomprising: compression means for compressing and coding said pluralityof pieces of data reproduced from said reproducing means; and means fortime-division multiplexing coded data from said compression means, saidencryption means being means for encrypting a time-division multiplexedsignal from said time-division multiplexing means.
 3. A receiving unitfor receiving main data transmitted from the transmitting apparatus asrecited in claim 1, said receiving unit comprising: means for receivingmultiplexed data transmitted from said transmitting apparatus; receivingdemultiplexing means for demultiplexing said multiplexed data receivedby receiving means to provide said main data, said initial value andsaid customer identifying code; receiving unit memory for storing anidentifying code and an arithmetic formula which are identical to thoseof this customer stored in said memory of said transmitting apparatus;arithmetic means for confirming reception of data requested fortransmission by this customer by collating said customer identifyingcode with said identifying code in said receiving unit memory andoperating said demultiplexed initial value pursuant to said arithmeticformula in said receiving unit memory to calculate a key signal;recording and reproducing unit for recording and reproducing said maindata; and first decryption means for decrypting said main data on thebasis of the key signal calculated by said arithmetic means to providesaid data requested for transmission.
 4. The receiving unit according toclaim 3 further comprising an IC card including said receiving unitmemory and said arithmetic means and detachably mounted to a main bodyof said receiving unit.
 5. The receiving unit according to claim 3further comprising: means for encrypting the key signal calculated bysaid arithmetic means by using the identifying code from said receivingunit memory; and means for multiplexing the key signal encrypted by saidencryption means and main data from said receiving demultiplexing means,said recording and reproducing unit being means for recording datamultiplexed by said multiplexing means.
 6. The receiving unit accordingto claim 5 further comprising: means for demultiplexing multiplexed datareproduced from said recording and reproducing unit into said main dataand said encrypted key signal; and second decryption means fordecrypting said encrypted key signal from said demultiplexing means onthe basis of said identifying code to provide said key signal.
 7. Thereceiving unit according to claim 3, wherein said recording andreproducing unit records said initial value and said main data, saidarithmetic means is means for providing said key signal by operatingsaid initial value reproduced from said recording and reproducing unitpursuant to said arithmetic formula read out of said receiving unitmemory, and said main data reproduced from said recording andreproducing unit is decrypted on the basis of said key signal calculatedby said arithmetic means.
 8. An apparatus for recording at leastencrypted main data and a key signal decrypting said encrypted maindata, comprising: a memory for storing an identifying code whichidentifies an individual customer, and an arithmetic algorithm set forsaid individual customer; an arithmetic circuit for calculating the keysignal by using said arithmetic algorithm, and an encryption circuit forencrypting the key signal by using said identifying code; a multiplexingcircuit for multiplexing said encrypted main data and said encrypted keysignal; and a recording circuit for recording said encrypted main dataand said encrypted key signal multiplexed by said multiplexer circuit.9. An apparatus for reproducing at least encrypted main data and anencrypted key signal decrypting said encrypted main data, from a storagemedium, said storage medium containing a key calculated by an arithmeticalgorithm that is specific to an individual customer, and encrypted byusing an identifying code specific to the individual customer, andfurther containing main data that have been encrypted using the key,said apparatus comprising: a demultiplexing circuit for demultiplexingsaid encrypted key signal from reproduced data; a memory for storingsaid identifying code that is specific to said individual customer; afirst decryption circuit for decrypting said encrypted key signaldemultiplexed by said demultiplexing circuit by using said identifyingcode; and a second decryption circuit for decrypting said encrypted maindata by using said key signal calculated by said arithmetic algorithm,which key signal has been decrypted by said first decryption circuit.10. An apparatus for transmitting at least encrypted main data and a keysignal decrypting said encrypted main data, comprising: a memory forstoring an identifying code which identifies an individual customer, andan arithmetic algorithm set for said individual customer; an arithmeticcircuit for calculating the key signal by using said arithmeticalgorithm, and an encryption circuit for encrypting the key signal byusing said identifying code; a multiplexing circuit for multiplexingsaid encrypted main data and said encrypted key signal; and an outputcircuit for delivering said encrypted main data and said encrypted keysignal multiplexed by said multiplexing circuit.
 11. An apparatus forreceiving transmitted data containing at least encrypted main datamultiplexed with an encrypted key signal decrypting said encrypted maindata, said transmitted data containing a key calculated by an arithmeticalgorithm that is specific to an individual customer, and encrypted byusing an identifying code specific to the individual customer, andfurther containing main data that have been encrypted using the key,said apparatus comprising: a demultiplexing circuit for demultiplexingsaid encrypted key signal from received data; a memory for storing saididentifying code that is specific to said individual customer; a firstdecryption circuit for decrypting said encrypted key signaldemultiplexed by said demultiplexing circuit by using said identifyingcode; and a second decryption circuit for decrypting said encrypted maindata by using said key signal calculated by said arithmetic algorithm,which key signal has been decrypted by said first decryption circuit.